(a) Field of the Invention
The present invention relates to a method for manufacturing a spherical BAM blue phosphor (BaMgAl10O17:Eu2+), and more particularly, to a method for manufacturing a spherical BAM blue phosphor particle that is preferable for embodying pictures having a high brightness. This is obtained by mixing raw materials with a melting agent (flux), followed by introducing the mixture into a closed reactor and heat-treating the mixture under a reducing atmosphere composed of nitrogen and hydrogen.
(b) Description of the Related Art
One of the major applications of phosphor is the field of display, in which the three primary visible colors, that is, red, green, and blue, are used to accomplish full color pictures. The three primary colors are generated when fluorescent materials (phosphors) are excited by external energies, such as through accelerated electron irradiation, ultraviolet radiation, an electron field, heat, etc. In general, phosphor is preferable for color display applications, as it has the unique property of high luminescence and high color purity of luminescence comprising the three primary colors. Phosphors are further desirable for this application as they have the property of high stability that can show little changes in optical properties during the heat-treatment and the chemical-treatment processes applied to parts of the display.
A commonly used method for coating phosphor particles onto the plasma display panel is the screen-printing method, in which the formulated phosphor paste is printed, forming thin phosphor layers within the discharge cells. In this process, highly packed phosphor layers are preferable for embodying pictures having high brightness. The shapes of coated phosphor layers are very much influenced by the shape of individual phosphor particles, the paste formulation, and coating process conditions. It is well known that spherically-shaped phosphor particles yield higher packing efficiency compared to non-spherical ones. Therefore, it is commercially viable for a company to be in the business of supplying phosphors that are spherically shaped.
Phosphors are ceramics generally manufactured by heating mixed raw materials at 600 to 1500° C. in order to complete solid state chemical reactions in either a batch-type or a continuous-type electric furnace under a controlled atmosphere. The melting agents (fluxes) are usually added to the mixed raw materials in order to facilitate the solid-state chemical reaction. The sizes and shapes of the resulting phosphors after high temperature reaction depend on both the heating schedules and the melting agents, that is, the flux systems, such as the types of flux materials and the amounts of flux.
The presently marketed BAM (BaMgAl10O17:Eu2+) is a blue phosphor wherein the mean particle diameter is from 2 to 10 micrometers, and the crystallinity of each particle is close to a single crystal. Recently, a demand for phosphors having well-controlled characteristics such as small and round particles has increased due to their superior performance in high resolution PDP applications.
Many efforts to manufacture round and small BAM blue phosphor particles have been made thus far, for example, sol-gel, hydrothermal, combustion, and coprecipitation methods.
The currently commercially available BAM blue phosphors for PDP applications, however, do not have the above-mentioned desirable particle characteristics. They are mostly either irregularly shaped or plate shaped. Although one of them shows a round morphology, its individual phosphor grain consists of several thin platy particles.
A manufacturing process of BAM blue phosphors patented by Matsushita is not preferable for obtaining BAM having the above-mentioned desirable particle characteristics due to the platy morphology of the products, because, even though they use spherically-shaped alumina as an alumina source material, they don't use any flux agents.
There is also a report for manufacturing BAM blue phosphor using pyrolysis methods. However, the methods results in platy phosphor particles instead of round-shaped ones.